[This project may not be active — check Github https://github.com/mozilla/chromeless]
Chromeless is a Mozilla Labs project in its early stages. The aim is to enable developers to create full blown desktop applications using only Web technologies. Chromeless apps have access to a collection of JavaScript APIs that provide them with deep desktop integration. One of the core capabilities of the Chromeless platform is the ability to safely embed untrusted Web applications inside these applications.
Chromeless vs Prism/WebRunner
Prism (an ex-Mozilla Labs project, now discontinued but kept going independently of Mozilla under the [now discontinued] WebRunner name) was/is a way to make Web pages superficially appear to be native applications. Firefox users could choose to turn a Web page into a "Prism application" and have an icon added to their desktop to launch it without the Firefox user interface surrounding the page. However, Prism "applications", being Web pages, were subject to all the normal restrictions that browsers place on a Web page. For example, Prism applications could not read/write files directly from/to the computer's file system. One of the ideas behind Chromeless is to remove these restrictions.